Bearing Life (L10) Calculator

Rating life of a rolling bearing in hours from its dynamic load rating, the load and the speed, with reliability adjustment and the rating needed for a target life.

How it works

The basic rating life L10 is the number of revolutions that 90 percent of a group of identical bearings reach or exceed before the first sign of fatigue of the rolling surfaces. It follows from the dynamic load rating C (the load for a life of one million revolutions) and the equivalent load P.

L10 = (C ÷ P)p million revolutions, L10h = 106 × L10 ÷ (60 n)

For a reliability above 90 percent the life is multiplied by the factor a1 (0.64 for 95 percent, 0.25 for 99 percent) and, following ISO 281, by a modification factor a23 for lubrication and contamination. The calculator also gives the rating C needed for a target life, which is how bearings are normally selected. Gears, shafts and bearing fits are in Gears and Power Transmission.

Worked example

A 6208 deep-groove ball bearing (C = 32.5 kN) carries a radial load of 3 kN at 1 450 rpm.

  • L10 = (32.5 ÷ 3)³ = 1 271 million revolutions.
  • L10h = 1 271.4 × 10⁶ ÷ (60 × 1 450) = 14 614 hours (1.7 years of continuous running).
  • At 95 percent reliability: 0.64 × 14 614 = 9 353 hours.
  • For a life of 20 000 hours the rating needed is C = 3 × (60 × 1 450 × 20 000 ÷ 10⁶)1/3 = 36.1 kN, so choose a bearing with C above that (for example a 6308 with 41 kN).
  • With a 1 kN axial load as well and X = 0.56, Y = 1.6: P = 0.56 × 3 + 1.6 × 1 = 3.28 kN and L10h = 11 182 hours: the axial load costs a third of the life.

Things to know

The rating life is a statistical life under the standard assumptions of clean lubricant and correct installation. Real bearings often fail from contamination, poor lubrication, misalignment or overheating long before fatigue.

The formula does not apply for heavy loads (P above about half the dynamic rating) where plastic deformation and the static rating govern, nor for very slow or oscillating motion (use the static rating C0).

For variable loads and speeds, calculate an equivalent load: P = (Σ (Pip × qi))1/p, where qi is the fraction of the time at each load.

The factors X and Y depend on the bearing type and on the ratio of axial to radial load: the catalog gives them (for deep-groove balls, X = 1, Y = 0 below the limiting ratio e).

Life is very sensitive to load: halving the load increases the ball bearing life eightfold. Speed affects the hours linearly.

Common questions

What does L10 mean?

The life that 90 percent of bearings of a group will reach or exceed. The median life is about five times the L10 life.

What is a dynamic load rating?

The constant load that a bearing can carry for one million revolutions with 90 percent reliability. It is given in the bearing catalog.

How long should a bearing last?

Typical design goals are 8 000 to 12 000 h for intermittent machinery, 20 000 to 30 000 h for industrial machines running eight hours a day, and 40 000 to 60 000 h for continuous operation.

Why does the roller bearing use 10/3?

The load-life relation depends on the contact geometry: line contact in a roller bearing gives a lower sensitivity to load than the point contact of a ball bearing.

Sources

  • ISO 281:2007, Rolling bearings: Dynamic load ratings and rating life; ISO 76 (static load ratings).
  • SKF, Rolling bearings catalog (life equations, factors a1 and aSKF); Harris, T. A. and Kotzalas, M. N., Essential Concepts of Bearing Technology, CRC Press.

Last reviewed: November 2, 2026